After a relay is mounted on an associated printed circuit board, which will be hereinafter referred to as pc board, terminals of the relay are electrically connected to the pc board, usually by means of soldering. After soldering, the pc board needs to be washed or cleaned to remove solder fluxes.
The washing is usually effected only on the soldered side of the pc board, and not on the other side on which is arranged the relay, so that only the soldered side of the pc board is put in a cleaning or washing liquid. This way of washing is rather difficult and troublesome, thus presenting an obstacle to an automatic washing operation.
However, if a so called "dip washing" method is used in which the pc board provided thereon with relays and/or another devices is entirely splashed or put in a washing liquid, the washing operation is simplified and automatic washing is possible.
However, in a conventionally known relay having a relay cover which is mounted on a base on which are arranged relay components, when the relay is entirely put in the washing liquid, the washing liquid can enter or penetrate into the relay where the base and the cover connect, since no special seal is effected between the base and the cover. The entrance or penetration of the washing liquid often results in faulty operation of the relay, such as failure to establish a complete electrical connection between contacts of the relay.
Alternatively, if the cover is completely sealed to the base of the relay to prevent the entrance or penetration of the washing liquid, any organic gas which may be produced inside the relay--for example, from a resin insulation of a relay coil or a resin coil bobbin when the coil is heated in operation--cannot escape from the relay and continues to stay therein. The organic gas also has an undesirable influence on the contacts of the relay.
As can be understood from the above discussion, in order to make "dip washing" possible, the relay not only must be completely sealed to prevent the washing liquid from penetrating or entering the relay when the latter is washed but also must be provided with an outlet or opening through which organic gas produced in the relay can escape during normal operation after the washing stage has been completed.
Japanese Utility Model Application No. 51-156977 (Laying Open Publication No. 53-74039) teaches one solution to this problem. In this prior application, the relay cover is provided with a closed hollow projection which can be cut after washing, so as to provide an opening for the organic gas to escape. According to this prior application, a relay is provided which can be "dip-washed" and from which interior organic gas can escape.
However, the provision of such a projection is not desirable, because, when the relays are packed, a bigger packaging box is necessary and the projections become obstacles when the relays are overlaid one on another. Furthermore, when the projections are cut, a cutting device is necessary and the cutting operations are troublesome.